This project is a continuation of our ongoing study of the transport of maternal anti-fetal antibodies through the human placenta and extraplacental membranes. The basic operating theory is that IgG attaches specifically to Fc receptors on trophoblast and amnionic epithelium, is internalized and passed through to the opposite side of the membrane. As the IgG is diffusing through the fibrous stroma antibodies to fetal antigens form complexes with antigen, are specifically adsorbed to macrophage Fc receptors, endocytosed and degraded. The remainder of the intact transported IgG passes into the fetal blood or amniotic fluid. This proposal is designed to prove the presence of antigen antibody complexes by indentifying antigen and establishing antibody specificity. Moreover, it is designed to characterize the trophoblastic Fc receptor, study adsorptive endocytosis by Fc receptor positive amnionic/trophoblastic cells and determine the route of IgG transport in a novel in vitro human IgG transport system. This will be the first time that it has been possible to look at mechanisms of IgG transport in the human either in vivo or in vitro.